COMPUTER-PROGRAMS THAT CALCULATE MANURE APPLICATION RATES

Decision support systems (DSSs) operated on personal computers are a c onvenient means to calculate application rates of livestock manures th at meet crop nutrient requirements and avoid excessive nutrient applic ations. Twelve DSSs that can be used to calculate application rates of dairy manure are described and compared. The major functions of the p rograms, their input data requirements, and their software and hardwar e requirements are described. The major functional differences between the programs, their nutrient availability assumptions, and user-frien dliness are discussed. The programs examined differ considerably in th e number of functions they perform. The simplest programs estimate man ure application rates for one field at a time. The more complex progra ms perform additional functions such as estimating the quantity of man ure, calculating application rates for multiple fields, automatically allocating the estimated amount of manure to those fields, and calibra ting manure spreaders. All of the programs use the same basic procedur e to calculate manure application rates. This is essentially: (i) crop nutrient requirements are estimated, (ii) manure nutrient (N, P, and K) content is entered by the user or estimated by the program, (iii) a vailability factors are applied to the manure nutrients, (iv) the rate of manure to supply available nutrients to meet crop requirements is calculated, and (v) rates of any supplementary commercial fertilizer a re calculated. The programs are typically developed for particular agr icultural regions. Four of the programs examined have regional adaptab ility, achieved by enabling the user to directly enter or to modify fa ctors used in calculating crop nutrient requirements and manure nutrie nt availability. DSSs have considerable promise in assisting with the many calculations required to determine manure application rates that meet crop nutrient requirements and minimize the risk of environmental pollution.